1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for tracking synchronization between wireless devices in a wireless communication system.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) evolved from a universal mobile telecommunications system (UMTS) is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) evolved from the 3GPP LTE.
Device-to-device (D2D) communication is a distributed communication technique in which neighboring wireless nodes directly deliver direct traffic. In the D2D communication, a wireless node such as a mobile phone autonomously discovers another wireless node which is physically neighboring thereto, and establishes a communication session and thereafter transmits traffic. The D2D communication can solve a traffic overload problem by distributing traffic concentrated to a base station. The D2D technique such as Bluetooth or Wi-Fi Direct directly supports communication between the wireless nodes without an aid of the base station.
It is necessary to consider a propagation delay between the wireless nodes when the D2D communication is designed. Although the Bluetooth supports data communication between wireless nodes separated by up to 100 m, an actual effective range is far less than that. When a distance between the wireless nodes is more increased, it is necessary to consider a path loss and a timing advance.